A kneading device has been used for kneading materials to be kneaded such as rubber and plastic. The kneading device generally includes a pair of rotors rotated in a kneading chamber, and kneads the materials to be kneaded into a predetermined state by the pair of rotors. Regarding the rotor of the kneading device, a flow of the materials to be kneaded around each rotor generated by rotation of the rotor is examined, and the shape of the rotor is set so that agitation, diffusion, and plasticization are balanced, for example. In connection with this, a batch-type kneading device in which a plurality of kneading blades is formed on the rotor has been known (see Patent Literature 1).
In the prior-art kneading device described in Patent Literature 1, the materials to be kneaded are kneaded by kneading blades composed of two long blades and two short blades while flowing. However, since the materials to be kneaded flow mainly around each rotor, it is difficult to knead the materials to be kneaded by effectively utilizing the entire space of the kneading chamber. Moreover, there is a concern that smooth flowing of the materials to be kneaded is disturbed by the kneading blades inclined in directions different from each other. In order to uniformly knead the materials to be kneaded by handling each of these problems, kneading time should be extended, but as the kneading time is extended, energy for kneading increases, which is a problem. Therefore, regarding the prior-art kneading device, there is a room for improvement in view of efficiency and quickness of kneading the materials to be kneaded.
Moreover, when rubber is kneaded with a filler (carbon, silica or the like), for example, the filler which is difficult to be mixed with rubber is necessary to be uniformly kneaded. In addition, in kneading requiring reaction between silica and its coupling agent, for example, it is preferable that kneading of the materials to be kneaded is completed before a temperature of the materials to be kneaded reaches a temperature (140° C., for example) at which a coupling reaction of the coupling agent starts. However, it is difficult for the prior-art kneading device to quickly knead the materials to be kneaded. Particularly in rubber for a tire, an added amount of silica has increased in recent years, and uniform kneading has become difficult.